Volume control method for radioreceivers



Oct. 23, 1934. J H BUSSARD 1,978 008 VOLUME CONTROL METHOD FORRADIORECEIVERS Filed Oct. 26. 1929 5 Sheets-Sheet 1 fi/a. men? fa 7 1NVEN TOR.

A WORN/5Y5 Oct. 23, 1934.

E. J. H. BUSSARD 1,978,008

VOLUME CONTROL METHOD FOR RADIORECEIVERS Filed Oct. 26. 1929 3Sheets-Sheet 2 our l, Jere-en Gr/c/ Va/frfyf 1 7 A ydhre F, lumen) Ju fyA TTORNEY$ Oct, 23, 134. E. J. H. BUSSARD 1,973,008

VOLUME CONTROL METHOD FOR RADIORECEIVERS Filed Oct. 26. 1929 3Sheets-Sheet 3 INVENTOR. a] 1% flaw Patented Oct. 23, 1934 UNITED STATESPATENT OFFICE VOLUME CONTROL METHOD FOR RADIOBECEIVE Application October26, 1929, Serial No. 402,771

14 Claims.

My invention relates to means for controlling the volume of output of a.radio receiver, and is perhaps chiefly applicable to multiple gridamplifier receivers, although it may also be used ti advantageously onsingle grid amplifiers. My volume control is applicable to radio tubesin which the filament supply is an unrectified or only partiallyrectified alternating current applied directly to the filaments, but isprimarily in intended for use with amplifier tubes in which the appliedcurrent is used to heat the emitting element or cathode and does notpass therethrough, or to direct current energized tubes.

With the filament type of A. C. radio tubes 15 it is usually impracticalto adjust the output volume or amplification factor of the tubes by amethod which changes the tube characteristics, due to the tendency ofthe tube to transmit the A. C. pulsations. It is possible, however,

with the heater type of tubes to adjust the negative bias of the grid,so as to control amplification. Thus an increase from normal, negativebias will reduce the amplification.

With tubes having two grids commonly known 5 as screen grid tubes, it isnot practical in some of the most desirable types of circuit to alterthe bias of either of the grids without at the same time affecting thebias of the other. The one grid, as a matter of fact, will so react to achange of bias of the other grid, as to partly compensate for thevariation in ,amplification which would otherwise result, or the controlgrid bias may drop sufficiently low to allow the tube to draw gridcurrent. This results in loss of selectivity and objectionable crosstalk, a feature which has been known to be serious enough to makereceivers impractical.

If itwere not for thiscompensating reaction 'of the tube net work, theideal amplification 40 control system for screen grid tubes would be toalter the normal potential of the screen grid with relation to thefilament or emitter.

In heater type, or D. C. screen grid tubes, it will accordingly bedesirable, in controlling the volume of output (by means that cut downamplification), to adjust the bias of both grids. My invention relatesto a mode of accomplishing such a double adjustment by a single controlelement. In the illustrated embodiment the control grid-filament returnand plate-filament return are applied to the screen grid-filament returnin an adjustable manner, the result being that as the screen grid plusbias is decreased the control grid minus bias is not decreased 5 or madepositive which would otherwise occur.

Indeed, the eflect otthe structure will be to impart a greater negativevalue to the control grid bias over the entire range than is usuallydesirable, so that while the use of my device is valuable for use asabove noted, I ordinarily employ a suitable by-pass, so that the controlgrid minus bias may be maintained constant over all or a desired portionof the range. It may be so arranged as to give gradually increasingcontrol grid bias to some predetermined value which will not result incomplete plate current cut off and rectification or detection in thesetubes, as this will give a very mushy and unpleasant reproduction, andis the maximum attenuation possible by means of increased grid bias. :0Usually the-control grid bias is not increased to more than about halfthis value as a maximum, and the remaining attenuation possible in thetube is accomplished by decreasing the screen grid voltage as far aspossible without causing mushy or garbled reproduction.

I accomplish my object in its preferred and simplest form by thatcontrol system to be hereinafter specifically described and the noveltytherein duly claimed.

In the drawings Figure l is a diagram of a heater type, screen grid tubenet work illustrating my invention.

Figure 2 is a diagram of a heater type tube net work, in which no screengrid is employed.

Figure 3 is a diagram of a. tube net work of filament emitter typewithout screen grid.

Figure 4 is a diagram of a tube net work in which the tube is offilament emitter type, with both control and screen grids.

Figure 5 is a diagram similar to Figure 1 but in which a shuntingresistance is employed.

Figure 6 is a chart showing the plate current and the control and screengrid voltages plotted against volume control as same is appliedaccording to my invention, with a dotted line showing the normaldrop ofcontrol grid voltage which would follow if resistance 10a were omitted.

Figure 7 shows my circuit in connection with a plurality of tubes;

Referring first to the arrangement shown in Figure 1the emitter l of thetube is energized by a heater indicated at 2. The control grid isindicated at 3, screen grid at 4, and plate at 5. The tuned circuit 6for the control grid is connected at its ground side to a sliderindicated at 7, this slider also carrying the negative return to theemitter of the D. C. plate supply.

The screen grid is connected to a selected point of a resistance 8, oneend of which is connected to the plate circuit 9 and the other end ofwhich is connected to the emitter through the usual biasing resistance10.

By connecting the control grid circuit or the ground potential(negative) by means of the slider to some point between the screen gridconnection and the emitter connection on the resistance 8, the negativebias of the control grid will be correct for the maximum amplificationof the tube. As the slider is moved toward the screen grid connectionthis negative bias will be increased. At the same time, however, thepositive bias between the screen grid and the emitter will be decreasedand brought near to the ground potential (negative) since with myarrangement the center arm of the potentiometer is at ground potential.

Referring next to the other views in which a like end result isobtained-in Figure 2 the indicating numbers are the same as in Figure 1for the several elements of the net work. The screen grid is, however,omitted, and the selected point on the resistance 8 is connected to thedirect current source of plate voltage, as by lead 11. In thisarrangement as the negative potential or ground is moved further fromthe emitter along the resistance 8, thus increasing the grid bias, thenegative plate return is brought nearer to the positive point, thuscutting down the potential difference between the emitter and the plate.

In Figure 3 the filament 1a is the emitter. The arrangement is otherwiselike that of Figure 2, with the same results.

In Figure 4 there is shown a case in which there is a screen grid, butthe filament 1a is the emitter. As will be noted, the arrangement inthis instance is a combination of the arrangement in Figures 1 and 3. Inthis view the resistance 8 is connected at one end to the screen gridlead, and the This variation in Figure 4 is merely another way of wiringthe receiver, and is the full equivalent to the arrangement in the otherdiagrams.

In Figure 5 the arrangement is similar to Figure 1 in which the positiveplate circuit lead is connected to the resistance 8. In addition, aresistance 12 is shunted across the biasing resistances, so as toprovide a leakage path for the direct current, that prevents cuttingdown the dinerence of plate potential with relation to the filament,beyond a certain amount.

In Figure 5 another variation over the other views that is ofimportance, is the use of the resistance 10a. The fixed biasingresistance 10 plus the variable biasing resistance at 8, cannot, in thearrangement of Figure 5, be eflective beyond a certain point, becausethe resistance 10a is in serted so as to by-pass the variableresistance.

In Figure 5 is the most complete and preferred arrangement of the network required for the best operating condition of my invention withscreen grid tubes. To the basic arrangement as shown in Figure 1 areadded the by-pass resistance 10a, and stabilizing resistance 12 shuntedfrom the plate circuit to the emitter providing a definite 12 servestoreduce this floating tendency to a minimum and permits the tube to beoperated nearer its maximum plate voltage with resulting maximumamplification.

Referring finally to the chart illustrative of the screen and controlgrid voltage changes, I have indicated the plate current screen gridvoltage and control grid voltage plotted against volume controlposition. Point C is the point of greatest volume, and point B is thepoint of greatest attenuation without signal distortion. At point D oncurve E, the control grid bias will begin to be so great that the platecircuit will exhibit rectifying action. Curve E is the control grid biasin a structure which omits the resistances 10a and 12 or theirequivalents.

While I have described my arrangement as applied to a single tube, itwill be apparent that it can be used as a common element in a series ofcoupled circuits. Figure 7 illustrates the device in connection with aseries of tubes.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is:-

1. A volume control method for application to screen and control gridradio tubes having a control grid to screen grid circuit and controlgrid to emitter circuit, which consists in changing the bias of thescreen grid while maintaining, substantially at full value, the minusbias of the control grid, by substantially inversely varying theresistances in a circuit including the control grid and the screen grid,and in a circuit including the control grid and the emitter.

2. A volume control method for application to plural grid tubes, whichconsists in changing the bias potential of one of the grids to controlthe volume output, and simultaneously changing the impressed biaspotential of the other grid to oil.- setda compensation change in thebias of said gri 3. A volume control method for application to pluralgrid tubes which consists in varying the normal potential of the screengrid with relation to the emitter and simultaneously compensating forthe reaction in the control grid circuit by changing the resistance inthe control grid circuit return, to compensate for the plate currentchange.

. 4. A volume control method for application to plural grid tubes whichconsists in varying the normal potential of the screen grid withrelation to the emitter and simultaneously compensating for the reactionin the control grid circuit by changing the resistance in the controlgrid circuit return, to compensate for the plate current change.

5. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to the highvoltage supply of one of the other elements of the tube and a connectionfrom said resistance element to the common return of the grid and platecircuits, said connection to the resistance being adjustably variablealong said resistance.

6. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to the highvoltage supply of one of the other elements of the tube and a connectionfrom said resistance element to the common return of the grid and platecircuits, said connection to the resistance being adjustably variablealong the said resistance, and a second resistance element connectedfrom the cathode to the high voltage supply of one of the otherelements.

7. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to thescreen grid of the tubes, and a connection from said resistance elementto the common return of the control grid and plate circuits, saidconnection to the resistance being adjustably variable along saidresistance.

8. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to thescreen grid of the tubes, and a connection from said resistance elementto the common return of the control grid and plate circuits, saidconnection to the resistance being adjustably variable along saidresistance, and a second resistance element connected from the cathodeto the high voltage supply of one of the other elements.

9. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to the highvoltage supply of one of the other elements of the tube, and a commonreturn of the grid and plate circuits having a connection to saidresistance, said connection being adjustably variable along saidresistance, and a fixed resistance in series with the adjustablyvariable connection and the said grid.

10. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to the plateof the tubes and a connection from said resistance element to the commonreturn of the grid and plate circuits, said connection to the resistancebeing adjustably variable along said resistance.

11. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to the plateof the tubes and a connection from said resistance element to the commonreturn of the grid and plate circuits, said connection to the resistancebeing adjustably variable along said resistance,

and a second resistance element connection from element to the commonreturn of the grid and plate circuits, said connection to the resistancebeing adjustably variable along said resistance, and a resistanceby-passing the said variable re' sistance.

13. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode to thescreen grid of the tubes, and a connection from said resistance elementto the common return of the control grid and plate circuits, saidconnection to the resistance being adjustably variable along saidresistance, and a resistance by-pass to the control grid from saidcommon return.

14. A volume control for radio circuits employing vacuum tubes, whichconsists of a resistance element connected from the cathode circuits tothe plate circuits of the tubes and a connection from said resistanceelement to the common return of the grid and plate circuits, saidconnection to the resistance being adjustably variable along saidresistance, and a resistance by-passing said adjustably variableconnection.

' EMMERY J. H. BUSSARD.

